Machines for forming coil springs from continuous wire are well known in the prior art. In the manufacture of mattresses and upholstered furniture that use arrays of coil springs, machines have been employed in the prior art that form a plurality of springs from a continuous length of wire. One such machine is disclosed in British Patent No. 1,327,795 to Willi Gerstorfer entitled "Improvements in or relating to Machines for the Manufacture of Compression Spring Strips from Wire, for example for Upholstery Inserts," expressly incorporated herein by reference. The machine of the Gerstorfer patent is operative to manufacture from a continuous length of wire a plurality of interconnected compression springs comprising alternate left and right hand coil springs joined by an integral straight length of wire. The machine of the Gerstorfer patent employs moveable linkages to shift the settings of the machine to coil the continuous wire alternately in first one direction and then the other, with each coiling direction being followed by the feeding of a length of straight wire. The linkages are cam controlled, with the cam shapes determining the pitch and radius of each spring coil and the length of each straight section of wire interconnecting the coils.
In the use of the machine described in the Gerstorfer patent, however, variations in the dimensions and metallurgical properties of the wire affect the dimensions and elastic properties of the coils formed of the wire, causing the spring dimensions to vary from spring to spring and from one coil to another. This variation can be reduced with wire of higher quality and price. In many applications, there is no need to control precisely the quality of the produced springs because the quality of the mattress or upholstery item in which they are used is not materially altered thereby, or because variations in the parameters of the springs can be compensated in assembly done by hand.
With the increased use of robotics and automated assembly of products using coil springs of the type referred to above, variations in the tolerances of the springs, which may be acceptable from the point of view of the quality of the final product, may not be tolerable for use in the automated assembly machinery that tends to rely on the components being in predictable locations and of predictable dimensions. This is particularly true of the relatively rigid straight lengths of wire which interconnect the elastic coils. Thus, there is a need for coil forming machines to accommodate variations in the quality of the wire from which coil springs are formed and variations in other parameters that cause variations in the dimensions or other properties of the manufactured springs, notwithstanding the precise repeatable movement of the coil forming machine elements.
In addition, in the coil forming machines of the prior art, such as those of the Gerstorfer apparatus referred to above, changes in the dimensions or other specifications of the springs being produced requires replacement or readjustment of mechanical machine components. Such a major changeover in the machine configuration, which replacement or readjustment of machine components entails, is time consuming, limits the flexibility of the machine, and adds cost to the use of the machinery for the manufacture of springs of differing specifications. Accordingly, there is a need for a spring forming machine that can more flexibly accommodate the manufacture of springs of differing designs.